1. Field of the Invention
The present invention relates to a radio transmitter such as portable terminal equipment and the like having a plurality of transmission modes, and its transmission power adjustment technology. Particularly, the present invention relates to a radio transmitter and its transmission power adjustment technology which quickly reduce a relative transmission power error among respective transmission modes.
2. Description of the Related Art
Conventional portable radio terminal equipment such as a portable telephone device and the like fixes its transmission mode during a telephone communication, and employs, in a few cases, a plurality of transmission modes while switching the transmission modes.
However, a high speed data rate communication such as High Speed Downlink Packet Access (HSDPA) system as a high speed transmission system in the portable telephone system has made an appearance. The HSDPA system employs multi-code for multiplexing a plurality of codes in one channel.
The HSDPA system changes a combination of a modulation system or an error correcting system. That is, the HSDPA system, when radio wave propagation condition is poor, employs a combination of a low speed Quadrature Phase Shift Keying (QPSK) modulation system and a low speed coding system with high error correction capability. While when the radio wave propagation condition is good, the HSDPA system employs a combination of a high speed 16 Quadrature Amplitude Modulation (16QAM) system and a high speed coding system with low error correction capability. Thus, the HSDPA system employs a plurality of codes with codes multiplexed into one channel by changing combinations of the modulation system and the error correction coding system according to the radio wave propagation condition.
In the case of the multi-code system, characteristics of the transmission signal vary caused by signal conditions such as the number of multiplexing, the modulation system or the like. Consequently, in order to employ a different transmission mode in accordance with the signal conditions, the multi-code system necessitates transmission power control according to the transmission mode.
At the time of high speed transmission, in the case that, for instance, sent is the signal with high transmission speed by using the multi-code system, the peak factor of the transmission signal becomes large, a distortion component of the amplifier output of the radio circuit becomes large, and the signal quality deteriorates. Therefore, high linearity of the amplifier or the like is demanded to minimize distortion. However, it is necessary to increase the amplifier current in order to improve the linearity of the amplifier. This increases power consumption, and transmission power, too.
Thus, the radio circuit using the HSDPA system is required to perform the transmission control being compatible to respective signal conditions according to the transmission mode. Therefore, its transmission signal power varies according to the transmission mode. Further, in the case of the HSDPA system, also, signal conditions differ greatly between an audio communication mode and a high speed data communication mode. Accordingly, it is necessary for the portable terminal to always control the transmission signal power into the optimum state when using a plurality of the transmission modes according to the signal conditions during communication.
Furthermore, a transmission circuit having such a plurality of transmission modes is required to minimize a relative transmission power error as small as possible among respective transmission modes, and to perform the transmission power adjustment in a short time, on the occasion of performing its transmission power adjustment.
A transmission power adjustment method conventionally carried out in the transmission circuit with a plurality of the transmission modes optimizes adjustment of the transmission power in respective transmission modes individually. Therefore, the radio transmitter having a large number of transmission modes cannot avoid increase of transmission power adjustment time.
Japanese Patent Application Laid-Open No. 2000-101456 (Document 1) has disclosed a radio transmission device provided with a first detection part and a second detection part at an automatic level control (ALC) part performing transmission power adjustment. The radio transmission device performs an ALC operation by obtaining a detection voltage from the first detection part at the time of low-output mode, and by obtaining a detection voltage from the second detection part at the time of high-output mode. The radio transmission device of the Document 1, thus, prevents breakdown of a detection diode on one hand, and sufficiently increases a level difference of transmission output in respective modes and attempts to reduce power consumption on the other hand.
However, the radio transmission device of the Document 1 increases the circuit size when the number of the transmission modes is large.
Further, Japanese Patent Application Laid-Open No. 2004-072556 (Document 2) has disclosed a transmitter and transmission power controlling method capable of stabilizing transmission power by compensating a change in diode detection efficiency due to temperature. The transmitter supplies a direct current bias voltage to a detection diode of the detection circuit to perform detection of the transmission signal, and measures and stores the detection output voltage. Further, the transmitter determines a difference between a stored detection output voltage and a current detection output voltage, and controls the gain of power control in a gain control circuit based on this difference signal. Thus, the transmitter of the Document 2 compensates a change in diode detection efficiency due to temperature to stabilize the transmission power.
However, since also the technology described in the Document 2, when the number of the transmission modes is large, generates control signals for each transmission power corresponding to each transmission mode, control becomes complicated and it takes much time for transmission power adjustment.
Furthermore, Japanese Patent Application Laid-Open No. 2004-235966 (Document 3) has disclosed a radio transmission apparatus in which constitution of a transmission power control part is simplified to reduce a mounting area. The radio transmission apparatus detects, at the time of transmission power adjustment mode, a transmission power level by receiving the transmission power at a receiving part to determine a control voltage of a variable gain amplifier circuit based on the detected level, and stores the control voltage into a memory. Then, the radio transmission apparatus optimizes, at the time of transmission mode, the transmission power by controlling the gain of the variable gain amplifier circuit by use of the stored control voltage. Since also the technology described in the Document 3, when the number of the transmission modes is large, generates control voltages for each transmission power corresponding to each mode, control becomes complicated and it takes much time for transmission power adjustment.